Filet the Amadai leaving the scales intact (or any fish with edible scales - most fish scales are not edible even when fried, so ask your fishmonger). Lightly salt both sides of the filet, and let rest in the refrigerator for 3-4 hours to let the salt penetrate.
Cut a large scallion or leek into a very fine julienne, slicing across the grain. Soak in cold water until ready to use.
Gently season 500mL of a light fish or vegetable stock to taste with a pinch of salt, 1/2 teaspoon light soy sauce, and 1 tablespoon fresh ginger juice. Reserve approximately 75mL of the seasoned stock in a small bowl and mix in 2 tablespoons of potato starch (or tapioca starch) to create a starch slurry that you will add back into the stock. To thicken the stock: Bring the seasoned stock to a light simmer in a small saucepan, and slowly add the reserved starch slurry to the simmering stock while stirring rapidly.
Add the julienned scallion to the sauce, and gently heat for about 5 minutes or until soft.
Skewer the fish with bamboo skewers (to prevent it from curling) and deep fry for 90 seconds at 180 degrees C, rest the fried fish on a paper towel to remove excess oil. Ladle the scallion sauce onto a pre-heated plate and place the fried fish on top of the sauce.